The invention relates to a chain wheel having pockets which serve to locate the horizontal links of a round steel chain, which only partly support the horizontal links and are each formed by four teeth, the flanks of which have a convex head part and a concave root part which adjoins the head part and has a rounded tooth-root section, the radius of curvature of which is essentially equal to half the thickness of the chain links, and also having an encircling groove which serves to locate the vertical links and subdivides the pockets in each case into two halves.
In known chain wheels of the abovementioned type, the rounded sections of the tooth roots which are also designated as tooth-root radii and are adapted to the contour of the chain links merge directly into the pocket bottom which forms an essentially flat bearing surface, provided with a recess in the area of the link sides, at least for the toric parts of the horizontal links (DIN draft 00 15 125, German Offenlegungsschrift No. 3,115,927). In other words, the bearing surfaces in the known chain wheels form tangential planes to an imaginary cylinder, the longitudinal axis of which coincides with the axis of rotation of the chain wheel.
Tests have shown that the known type of support is not without its problems. This is because, as a result of frictional wear caused by relative movements between the chain wheel and the incoming horizontal links, wear hollows form in the area of the pocket bottoms which adjoins the rounded tooth-root sections. Although these wear hollows do not constitute a serious risk to the chain wheels, they do constitute a serious risk to the horizontal links. The reason for this can be seen from the fact that the vertical links attempt to press the horizontal link parts located in the area of the wear hollows into the wear hollows. At the same time, the edge of the wear hollows which faces the center of the pocket bottom forms a type of tilting edge which leads to bending stresses in the horizontal links which can cause fractures in particular at higher loads.